Abstract. Despite the acknowledged relevance of aerosol-derived water-soluble organic
carbon (WSOC) to climate and biogeochemical cycling, characterization of
aerosol WSOC has been limited. Electrospray ionization Fourier transform ion
cyclotron resonance mass spectrometry (ESI FT-ICR MS) was utilized in this
study to provide detailed molecular level characterization of the high
molecular weight (HMW; m/z>223) component of aerosol-derived WSOC
collected from rural sites in Virginia and New York, USA. More than 3000
peaks were detected by ESI FT-ICR MS within a m/z range of 223–600 for
each sample. Approximately 86% (Virginia) and 78% (New York) of these
peaks were assigned molecular formulas using only carbon (C), hydrogen (H),
oxygen (O), nitrogen (N), and sulfur (S) as elemental constituents. H/C and
O/C molar ratios were plotted on van Krevelen diagrams and indicated a
strong contribution of lignin-like and lipid-like compounds to the
aerosol-derived WSOC samples. Approximately 1–4% of the peaks in the
aerosol-derived WSOC mass spectra were classified as black carbon (BC) on
the basis of double bond equivalents calculated from the assigned molecular
formulas. In addition, several high-magnitude peaks in the mass spectra of
samples from both sites corresponded to molecular formulas proposed in
previous secondary organic aerosol (SOA) laboratory investigations
indicating that SOAs are important constituents of the WSOC. Overall, ESI
FT-ICR MS provides a level of resolution adequate for detailed compositional
and source information of the HMW constituents of aerosol-derived WSOC.